1. Field of the Invention
The present invention relates to an internal combustion engine having a supercharging system, e.g., exhaust-gas turbocharger.
2. Description of the Related Art
Increasingly, internal combustion engines are provided with supercharging systems to increase the amount of air suppliable to the internal combustion engine. This may substantially improve the power and efficiency of the internal combustion engine.
As a rule, supercharging systems have a turbine which is situated in an exhaust gas section of the internal combustion engine. The turbine is coupled to a compressor in an air supply section via a suitable mechanical system in such a way that a rotation of a turbine wheel of the turbine is converted into a rotation of a compressor wheel of the compressor. The turbine wheel and the compressor wheel are usually connected to each other by a shaft.
With the aid of the supercharging system, a boost pressure is set on an output side of the compressor by using an actuator adjustment to influence either the amount of exhaust gas flowing over the turbine of the supercharging system or the turbine efficiency, e.g., with the aid of a variable turbine geometry.
Since the rotational speed of the supercharging system driven by exhaust gas enthalpy largely depends on the exhaust gas enthalpy, the maximum permissible rotational speed of the supercharging system may, under some circumstances, be exceeded, depending on the operating mode of the internal combustion engine. Exceeding this rotational speed usually destroys the supercharging system. In particular, supercharging systems having small turbine and compressor wheel diameters, which have an improved angular acceleration performance due to a low moment of inertia, may very quickly exceed the maximum permissible rotational speed in dynamic situations. For these situations, it is desirable to control or regulate the rotational speed of the rotor assembly of the supercharging system to enable improved protection against an excess rotational speed.
Moreover, in the case of two- or multi-stage supercharging due to series- or parallel-connecting supercharging systems having different characteristics, it is particularly useful to regulate the supercharging systems as a function of their rotational speed.
The rotational speed of turbochargers can be detected, e.g., as described in published PCT international patent application document WO 2006/045680 A1, with the aid of a magnet attached to a shaft of the rotor assembly, whose rotation is detected along with the rotational speed of the shaft, using a Hall element on the compressor housing. Alternatively, as described in published PCT international patent application document WO 2005/012919 A1, a rotational speed detection system may be provided which detects eddy currents produced by the motion of the compressor blades in a stationary magnetic field, using a GMR element.
Furthermore, it may be necessary to monitor the temperature of the supercharging system. After all, depending on the operating point of the internal combustion engine, a very high temperature may occur, which may damage the supercharging system.
A temperature detection system for a supercharging system is known from published German patent document DE 10 2006 021 430 A1. The fact that impermissibly high temperatures of the supercharging system are avoidable by monitoring the temperature is described therein. In particular, the supercharging system may be operated as a function of the detected temperature in such a way that its temperature may be lowered, e.g., by reducing the boost pressure or by correspondingly activating an electric radiator fan. The rotational speed is detected with the aid of an integrated circuit which is used to evaluate the rotational speed sensor signal, and with the aid of a diode which has a temperature-dependent current-voltage characteristic. As a measure of the temperature of the supercharging system, an indication may thus be provided about a voltage drop via the diode. It is possible to switch back and forth between detection of the rotational speed sensor signal and the temperature detection with the aid of the diode to provide either a rotational speed indication or a temperature indication by the integrated circuit.
The disadvantage of this approach is that it requires a relatively complex circuit in the integrated circuit to carry out the switching operation between the analog variable of the voltage drop as the temperature indication and the provision of the rotational speed sensor signal. Furthermore, the control unit which evaluates the information provided by the integrated circuit must be suitable for evaluating the analog temperature indication.
If is therefore an object of the present invention to provide a method and a device for easily providing a rotational speed indication and a temperature indication for a supercharging system, the complexity for providing the rotational speed indication and the temperature indication in a control unit, which is separate from the supercharging unit, being reduced.